This invention concerns a method to butt bars. The invention concerns also a butting assembly which employs such method. The bar butting assembly according to the invention is applied advantageously in cooperation with, and upstream of, machines fed with a bar or a bundle of bars, such as bending machines or machines to shear bars into segments of a pre-set length, for instance.
The machines have the purpose of producing accurately bent stirrups and bars and especially stirrups and bent bars for building work; the machines are therefore especially suitable for processing round bars for building work with a smooth outer surface or with ridges to accentuate fixture in concrete.
Various types of assembly to butt bars are disclosed in the state of the art. FR-A-2.472.523 discloses a bending machine which includes butting and lengthwise feeding means consisting of a thrust block, which is thrust against the trailing end of a bundle of bars so as to make the leading end of the bars cooperate with an abutment stop.
This machine does not ensure a correct butting of the bars inasmuch as it causes the trailing ends of a bundle of bars to be aligned but, owing to the length of the bars not being always constant but being affected by the tolerances of the operation of shearing the bars to size, does not ensure a correct butting of the leading ends of the bars. FR-A-2.340.152 discloses a device to feed bars lengthwise, whereby the butting is performed by engaging the bar and feeding it lengthwise, by a winch for instance, until the leading end of the bar has been brought into contact with an abutment plate suitably arranged beforehand in the required position. This system requires that the feeding means should pre-arrange the bars one by one in the shearing position and should therefore have a considerable travel, which will vary according to the length of the bars to be produced.
EP-A-0.188.850 arranges that a bundle of unbutted bars clamped by longitudinally movable gripper means is fed forwards until it cooperates with an abutment plate actuated by a piston; this plate has a first advanced position and a second retracted position. The leading end of the bar in its advanced position cooperates with the abutment plate and displaces the plate from its first advanced position to its second retracted position.
The gripper is then opened to free the bundle and retreats to its starting position, while the piston is actuated to bring the abutment plate to its first advanced position.
The abutment plate then brings the bars forwards again and butts them. This operation is repeated even with a great number of cycles.
This system entails the drawback that there are no checks to ensure that the whole bundle has been properly butted, and a machine operator has to be present to control the correct butting of the bundle of bars visually, thus increasing the costs of the operation.
To eliminate the presence of the machine operator, a cycle can be arranged whereby the butting operation is repeated automatically a great number of times, which can be determined as required.
But this solution not only does not provide an absolute assurance of correct butting of the bundle of bars but also leads to a great lengthening of the butting cycle and requires a consumption of energy greater than that strictly necessary and therefore increases the costs of the butting operation. U.S. Pat. No. 3,911,770 concerns a cutting machine to cut small segments, one at a time and all of the same length; from a smooth, gauged bar; it therefore does not concern a butting assembly which prepares butted bars or bundles of bars for a shearing machine or bending machine.
The cutting machine of this prior art document includes a bar feeder to position the leading end of the bar beyond the cutting means so as to make that end cooperate with an abutment stop, the pre-set distance of which from the cutting means determines the length of the segments to be cut. The segments are then removed by means of a chute after the abutment stop has of necessity been temporarily disactivated. The removal is made possible by two accompanying factors, the disactivation of the abutment stop and the feed of the bar. This teaching can be used only with small pieces of material having a constant and accurate cross-section in one single bar.
FR-A-2.205.386 includes a trolley able to move parallel to the axis of feed of bars and equipped with grippers to engage the single bar to be butted.
The trolley has a rear end-of-travel stop which can be positioned as required and the contact of which with the trolley causes disactivation of the motor of the trolley and therefore the halting of the trolley and the shearing. In this position the engagement grippers open and let the bar fall.
The butting can therefore never be accurate since the distance from the end of the bar to the point of engagement of the grippers is not the same for all the bars, so that the bars are in fact not butted precisely.